That debate may now be over: Theta sweeps serve both functions, depending on the situation, according to three new studies by independent teams. Theta sweeps occur within individual theta wave cycles, which are around 125-250 milliseconds long. Together, the studies show how theta sweeps begin to plan an animal’s next steps rather than sampling the world, says Redish, who was not involved in the work. “It’s really exciting to see how the field is really converging on mechanisms and circuits that can drive [theta sweeps].” And theta sweeps continued during REM sleep, switching between passive left-right sampling and more narrow, attention-like sweeps, the study found.